1. Field of the Invention
The present invention relates generally to stimulating medical devices, and more particularly, to determining operating parameters for a stimulating medical device.
2. Related Art
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person may have hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways that provide sound to hair cells in the cochlea are impeded, for example, by damage to the ossicles. Conductive hearing loss is often addressed with conventional hearing aids which amplify sound so that acoustic information can reach the cochlea.
Profound deafness, however, is caused by sensorineural hearing loss. This type of hearing loss is due to the absence or destruction of the hair cells in the cochlea which transduce acoustic signals into nerve impulses. Those suffering from sensorineural hearing loss are thus unable to derive suitable benefit from conventional hearing aids. As a result, prosthetic hearing implants such as cochlear™ prostheses (commonly referred to as cochlear™ prosthetic devices, cochlear™ implants, cochlear™ devices, and the like; simply cochlear implants herein) have been developed to provide persons with sensorineural hearing loss with the ability to perceive sound.
Cochlear implants traditionally comprise external and internal components that cooperate with each other to provide sound sensations to a recipient. The external component traditionally includes a microphone that detects environmental sounds, a sound processor that selects and converts certain detected sounds, particularly speech, into a coded signal, a power source such as a battery, and an external transmitter antenna.
The coded signal generated by the sound processor is transmitted transcutaneously to an implanted receiver/stimulator unit, commonly located within a recess of the temporal bone of the recipient. This transcutaneous transmission occurs via the external transmitter antenna which is positioned to communicate with an implanted receiver antenna disposed within the receiver/stimulator unit. This communication transmits the coded sound signal while also providing power to the implanted receiver/stimulator unit. Conventionally, this link has been in the form of a radio frequency (RF) link, although other communication and power links have been proposed and implemented with varying degrees of success.
The implanted receiver/stimulator unit also includes a stimulator that processes the coded signals to generate an electrical stimulation signal to an intra-cochlea electrode assembly. The electrode assembly typically has a plurality of electrodes that apply electrical stimulation to the auditory nerve to produce a hearing sensation corresponding to the original detected sound. Because the cochlea is tonotopically mapped, that is, partitioned into regions each responsive to stimulation signals in a particular frequency range, each electrode of the implantable electrode array is positioned and configured to deliver a stimulation current to a particular region of the cochlea. In the conversion of sound to electrical stimulation, frequencies are allocated to stimulation channels that provide stimulation current to electrodes that lie in positions in the cochlea at or immediately adjacent to the region of the cochlea that would naturally be stimulated in normal hearing. This enables cochlear implants to bypass the hair cells in the cochlea to deliver electrical stimulation directly to auditory nerve fibers, thereby causing the brain to perceive hearing sensations resembling natural hearing sensations.
The effectiveness of a cochlear implant is dependent not only on the device itself but also on the manner in which the device is customized to conform to the hearing characteristics of a specific recipient. This customization process, commonly referred to as “fitting,” “programming,” or “mapping,” involves the collection and determination of certain operating parameters of the device. These operating parameters include, for example, recipient-specific parameters such as the minimum stimulation current level required to evoke a neural response at a given stimulation channel, known as the threshold level (commonly referred to as the “THR” or “T-Level;” “threshold level” herein), or recipient-specific parameters such as the level at which a sound is loud but comfortable, known as the maximum comfort level (commonly referred to as the Most Comfortable Loudness Level, “MCL,” “M-Level,” or “C-Level;” simply “comfort level” herein) for each stimulation channel. The threshold and comfort levels, and perhaps other operating parameters, are utilized by a cochlear implant to adjust the stimulation current to attain a desired level of stimulation for a particular recipient.